I promise
by AryYuna
Summary: [SPOILERS SEASON TEN] He wouldn't lose his brother. Not again. Episode 10x09 "The things we left behind" coda.


_I'm having mixed feelings about this season: on one hand, I find the Mark of Cain arc fascinating, but on the other hand I have next to no faith in Carver&Co to not screw it up. But I'm not gonna throw myself into a two pages rant about how unprofessional saying "when we write a cliffhanger we don't know what's gonna happen next" is: for once, I wanna express my appreciation for an episode._

_The mid-season finale was _unexpectedly_ beautiful: no matter my hatred for anything not-Winchester, I loved this return to a Castiel _with a purpose_ and even Claire looked less like a cartoon character than like ninety percent of Carver&Co's characters. And then there was that beautiful John moment that made me so happy I could cry._

_An episode this good _deserved_ a fanfiction, right? So I started plotting this story as soon as credits rolled in (__and after reblogging like thirty posts about John on tumblr XD)__._

_I apologize for my English; it's not my first language and I don't have a beta-reader. If you find any mistakes, please let me know and I'll see to fix them._

_You can find this story in Italian here: __wwwDOTefpfanficDOTnetSLASHviewstoryDOTphp?sid=2958893_

**Disclaimer:**_ unfortunately, SPN doesn't belong to me. If it did… well, I would meet Jensen Ackles e Jared Padalecki, which would be veeeery good, and there would be someone reminding the authors about _canon_…_

* * *

><p><strong>I promise<strong>

"Tell me you _had_ to do this."

"I-I didn't mean to."

"No. Tell me it was them or you!"

Dean didn't reply.

Sam lowered his hands from his brother's face; he was panting as if he'd run for miles, in short, heavy gasps. He didn't want to look at the sea of blood surrounding them, but he couldn't hold his brother's empty stare, the darkness behind his green – _fucking green, not black anymore!_ – eyes.

His hand lingered on Dean's shoulder, as if to give him comfort. But how could he? The bloody mess they were immersed into had been created by his brother – _his brother_ – eaten by the darkness of the symbol marking his arm. The symbol Sam hadn't been able to erase yet, even though he'd tried.

He let his hand slip down.

Sam thought he'd have more time. He always thought he'd have more time, and that was his biggest mistake: he'd thought that with Jessica, and had put off the proposal for which he'd already bought the ring: he had wanted to tell her the truth _before_ asking her to spend their lives together, and he had just lacked the courage; he'd lost her before he could find it. He'd thought that with John, and he'd lost his father as well before he could get over the pride preventing him from giving and asking for forgiveness, from taking a step towards a more equal relationship. He'd even thought that with Amelia, even though he'd been older, wiser; even though he should've been a veteran of lost chances. It wasn't the supernatural that had taken her away from him, but he'd lost her as well; because he hadn't wanted to tell her the truth, postponing it every day of the year they'd spent together.

And now… now he'd lost his brother, _again_, because he'd been unable to find a solution faster, because maybe he hadn't searched enough, pating more attention to his pride than his love for Dean.

He heard Castiel and Claire's steps leaving the room – Cas was taking the shocked girl outside – and took a deep breath to gather the courage and face that umpteenth hit.

He reached up again and closed one hand on his brother's shoulder, expressing with that gesture his support, while he gently took the bloody knife from Dean with the other.

"We'll fix this as well, Dean. _Together_," he added, because he knew it would mean everything to his brother.

The older man looked up, but his gaze was hollow, lost. Sam ignored the knot taking his breath away for a moment and stood up, his hand still on his brother's shoulder. "C'mon," he said, and Dean followed him as if in a trance.

On the outside, Claire looked calmer, but kept her eyes away from the Winchesters.

"Cas," Sam said, "you mind driving?"

The angel looked at him, confused, that at Dean; the older hunter didn't look as if he was aware there was someone with him, he just kept staring at his blood-stained hands. He didn't even rouse when Sam took the keys for the Impala from his jacket. It was disturbing, seeing him that passive about his baby driven by someone who wasn't him or his brother.

"Sure," Cas replied with a frown, worried about his friend.

He took Claire to the Impala and had her get in the passenger seat, taking his place behind the wheel. When all four of them were in the car, he turned the engine on.

"Where to?" he asked. Sam opened his mouth to reply, but Claire preceded him.

"Castiel, I appreciate what you did for me, but… I'm not gonna come with you, if that's what you're expecting. You didn't come for me when I prayed for you, when I was a kid and I needed help; I don't need a father anymore – or an angel pretending to be a father. I can take care of myself," she angrily said.

"Claire…" Cas began, but he didn't know what to say. "You cannot stay here, Claire: the police will find…" he stopped. After taking a deep breath, he went on, "You do not have a place to stay, or Randy and Dustin, anymore. And if the police finds you before social services…"

He didn't need to finish: Claire knew what would happen if the police found the bodies. She lowered her head.

"Let's go to the bunker. There, Claire will be safe… and we can decide what to do," Sam answered. Dean didn't say anything, still staring at his hands as if they were the center of his world.

Castiel looked up in the rearview mirror and nodded.

"Okay."

* * *

><p>Claire fell asleep curled against the door. Castiel pulled over for a minute to shrug his trench coat off and cover her with it, then resumed driving. Behind them, Sam was washing his brother's hands with a handkerchief he'd wet with holy water. Dean still looked lost in his thoughts, miles away from what was around him.<p>

They got to Lebanon, Kansas in the early morning; the streets were almost desert. They passed through the town to the Men of Letters' bunker, and Cas drove around to get in the garage.

When he turned the engine off, Claire woke.

"Where are we?" she asked rubbing her eyes.

"Somewhere safe."

The girl frowned, but followed the angel when he got out of the car, determined to not remain alone with the Winchesters.

Alone with his brother, Sam climbed out as well and walked to the other side to open Dean's door. The older man looked up at him for a moment before climbing out and following him through the corridors to his room. Sam was disturbed by how pliant –_ absent _– he was.

"Rest up; it's been a long hunt – even if it's not been a proper _hunt_." Dean sat on his bed, but didn't answer. Sam gently pushed him to make him lie down and untied his brother's boots, worried by that silent obedience. "We'll fix everything. I promise," he said at last, even though he knew he had no right to. He then turned and left the room.

He went back to the garage to take his duffel from the Impala's trunk and brought it to the library, where he dropped it on the floor after retrieving his laptop to start – _resume_ – his research. Castiel joined him a short time later.

"Claire okay?"

The angel nodded. "She is happy for the chance to have a shower, even though I had to reassure her that nobody would disturb her. She seemed more at ease once she discovered the doors can be locked from the inside." Sam raised an eyebrow. "It was not an easy night, for her. And she does not know you – _us _– enough to give her trust, after what happened; after what she saw." The younger man lowered his gaze. Castiel sat beside him. "How is he?"

Sam shook his head.

"He didn't say a word."

"Dean is not a murderer," Cas gently said, ignoring Sam's flinch. "And he's still, at least in part, himself."

"So he's not enough _human_ to control himself, but he's human enough to feel guilty about what he does. Sweet," Sam snorted with no humor.

"Sam." Cas' tone drew his attention. He felt an odd anxiety rising inside him. "There is something you should know." _No. I don't want to. Whatever it is, I don't want to._ The young man nodded, even though the thing he wanted the most at that moment was running away. "When we met in Pontiac – while you were speaking to social services – Dean asked me something." The angel took a deep breath, his gaze wandering among the tall dark wood shelves, filled with ancient books. He was trying to avoid Sam's eyes, and that unsettled the young man even more. "He asked… If he were to go dark side… He asked me to kill him."

There was a pendulum clock, somewhere in the main area of the bunker. Its ticking was really annoying, even more so because the noise was amplified by the tall ceilings and wood planking on the walls. You'd expect more quiet in a library.

"What?" Sam asked, bewildered.

Castiel closed his eyes.

"He does not want to become a demon. Dean has fought evil all his life; the thought of…"

Sam suddenly stood up, sending his chair crashing against the floor; the noise bouncing between the walls drowned for a moment the hated ticking.

"How _dare_ he!" he yelled, kicking the duffel he'd left on the floor next to the table. "He can't give up! He can't _even think_ of giving up like this! Not like fucking this!" He clenched his fists, looking around for something to punch. It wasn't his usual way of dealing; Sam was more the kind of person who vents his anger through yelling rather than through violence against lifeless objects; that had been his MO since he was a kid and had started fighting with his father: Sam yelled, John yelled – and Dean found himself involved despite himself, even though he was just trying to reconcile them. In the end, Sam and John went back to talk to each other in a civil – and gradually more loving – manner, until their next fight; Dean, on the other hand, was more the type to vent his anger through killing the creatures they hunted or finding a girl that was looking for a hot night, no strings attached.

At that moment, though, Sam didn't have anyone to yell at, but he needed to vent the frustration and pain he felt at the thought of losing his brother – this time by… what, suicide by angel? "I won't let him give up. We can fix this too, like we fixed everything else. We'll remove that damned Mark, he'll be himself again. I know there is a solution, and I'll fucking find it!"

Castiel didn't reply. He sat at the table, his eyes calm, thoughts unreadable. Sam found his relief valve.

"You had no right to make that promise," he started. Cas, though, wasn't a human as John had been: he was an angel, and angels don't give in to anger that easily. "I won't let you hurt him, angel or not. Dean is my brother, and I won't even let you get close to him, if you think you can…"

… Or maybe angels could get mad as well, you just needed to push the right buttons: Castiel stood up in a more fluid and graceful movement than Sam, but no less fast, and was in his face in a heartbeat.

"Don not dare thinking for _a moment_ I want to harm your brother, Samuel," he said in a low and icy voice. "I could never," he hissed, his face a couple of inches away from Sam's. He suddenly looked more similar to the celestial being he'd been when they'd first met him, than to the friend that'd fought by their side in the latest years. "I did not promise him anything because I knew I could never keep such a promise."

No matter his superior height, Sam lowered his voice like a duly reprimanded kid – even though it'd started in a different way, their argument had ended _exactly_ the way his first fights with John had, before teenage years taught him to turn his back and slam the door – and nodded.

"Good," the young man said, unable to not have the last word. He hated not being able to be in control of the situation, and that was happening more and more often, lately.

Cas took a step back; his vessel's blue eyes held a soft look.

"We will find a solution. Together," he said, unconsciously using almost the same words Sam had told his brother in Randy's house.

He just hoped a solution existed.

* * *

><p>With Castiel's help, the younger Winchester resumed his research about the Mark of Cain: the two of them took books from the shelves, flooding the already crowded table, discarding then volume after volume 'cause…<p>

There was nothing. Absolutely nothing.

Not that Sam was expecting to magically find something in a few hours when he'd been unable to in months, but there was always that tiny part of him that didn't want to give up, that wanted to believe Castiel's presence would make a difference. But not even angels seemed to know anything about the Mark of Cain: the demonic symbol had vanished from history along with Cain, believed to be dead in the great battle in which – according to lore – the archangels had killed the Knights of Hell. They now knew the battle never happened, and that Cain himself had killed the Knights, but for centuries the version spread to the lower orders of angels had been about Heaven's victory over Hell; and that meant that Cas could only offer an extra pair of eyes to read books written by men who didn't know any more than them.

Around lunchtime, Claire entered the library with faked casualness, her curious gaze jumping from shelf to shelf, her hesitating gait betraying her apprehension for being in an unknown place with dangerous men.

Cas smiled at her and closed his book.

"Claire. I guess you will be hungry," he told her in a kind voice. The girl started as if she wasn't expecting them to notice her, even though she stood a few feet from the table where Cas and Sam were – fruitlessly – researching.

She quickly hid her surprise painting a cocky expression on her face. Her rigid pose said something very different, though.

"I'm not hungry. I just wanted to ask for a ride to the bus station," she said, determined. She sounded as if she'd prepared her lines, after her first failed attempt of the night before.

Cas frowned.

"Claire… You can't go alone."

"That's why I asked for a ride to the bus station. I'm not even sure where we are, I couldn't get there on my own," she replied, and it was _clear_ she's thoroughly considered all possible objections to her request and the best answers to them.

"And what then? What's your plan?" Sam intervened, finally closing his book as well.

"That's none of your business." The girl took a deep breath and straightening her back, raised her chin. "I appreciate your help; if you hadn't gotten there when you did, things could've gone really bad for me." _Euphemism._ "But I can take care of myself, and it's time for me to go."

"Claire, you're just…" Cas tried to make her see reason, but she stopped him.

"Just a little girl? You should've thought about that _before_ taking my Dad away, don't you think Castiel?" Her voice was low and controlled, her clenched fists the only sign of how _not_ calm she really was. "I can take care of myself; I've been doing it for years. Now, if you could please take me to the bus station I would really appreciate it. Or, you could at least tell me how to get there?"

Castiel looked at Sam for help: he wanted to help the girl, he felt responsible for her – it was true it'd been his fault that Claire had lost everything; he'd taken away her father and mother. Sam, for his part, needed Cas' help because his brother's life was at stake, and that trumped anything else – including the real problems of an innocent teenager with a life destroyed by the supernatural.

"I can take you there," the younger Winchester said, gaining a confused look from Castiel and a half-smile from Claire. "But consider this, first: do you have a place to stay? Someone to take care of you? You're underage and have a past of theft and minor crimes; when the police finds Randy and those other men's bodies, what you think they'll do? How will you convince them you and Dustin have nothing to do with it?"

He spoke calmly and looking straight at her, and the girl lowered her gaze.

"I don't doubt you can take care of yourself, but you don't need to; not now, at least. Wait for a while, stay here until you can find something better, or until… until the dust settles and you can get back to Pontiac, if you want to." He didn't ask her to give a second chance to Castiel, because he knew personally how hard it was being objective and ignoring your teenage natural cockiness.

Claire was quiet. After a few seconds she sighed and nodded, but didn't move.

"I will go prepare something to eat," Cas interrupted the stillness. "Sam, you need a break. _You do_," he insisted when he saw the young man trying to object. "It will do you good: you will be more focused when you get back to work."

Sam looked at him, annoyed, but in the end he complied. He slowly got up without looking at anyone and took the corridor to the dormitory area. He heard the girl talk with Cas, ma couldn't discern their words.

Further down the corridor, though, he heard something else. Sam stopped, listening; when he was able to detect its source, he quickly covered the few feet that separated him from the bathroom. He surpassed his brother's room, distractedly noticing the empty and undone bed, and stopped outside the bathroom.

"Dean?" he called, unsure, knocking softly. From the inside he could hear groans. "Dean? Can I come in?" He didn't receive a reply, but pushed the door open nonetheless.

He found Dean on his knees before the toilet bowl, head lowered, white-knuckled hands holding the porcelain hem. His sweated back trembled for the effort of throwing up.

"Hey," he said touching his hand to his brother's shoulder and getting to his knees in the narrow space. Dean didn't answer, focused on vomiting the – lots of – food he'd ingested the night before. Sam moved his hand up and down his brother's back, giving him support. When the heaving finally subsided, Dean slowly raised his head and Sam started.

His eyes were glazed and tired, his face pale. There were specks of blood on his lips.

"Dean? Are you okay?"

Stupid question. Nobody throws up blood, if they're okay.

"I'm fine," his brother confirmed, and Sam felt relieved; not because he believed Dean, _far from it_, but getting an answer was a big step forward: the almost catatonic version of his brother that had come back to the bunker with him had unsettled him more than he could imagine, and Sam hoped to never see it again. Nothing should have the power to affect Dean Winchester that much.

"That's blood," Sam pointed out. _No shit, Sherlock._

Dean brought his hand to his lips and looked at the red spots on his fingers.

"Uh," he answered. "It's nothing."

The younger brother raised an eyebrow.

"It's blood, Dean. It's supposed to stay on the _inside_ of your body, not on the outside."

Dean closed his eyes, and Sam feared he was about to pass out. He moved his hand from his brother's back to his shoulder, to hold him if necessary. "It's another side effect," Dean murmured.

To Sam, it was like a slap right in his face.

"Of… Of the Mark?" he stupidly asked.

Dean avoided his eyes and didn't answer.

They stayed like that, kneeling of the cold bathroom floor, in the constricted space between the wall and the toilet. At last, Sam stood up, his hand still on his brother's shoulder. "C'mon," he only said, and Dean followed him. He swayed for a moment when he got to his feet, but his brother's firm hold allowed him to regain his balance. Slowly, they got out of the bathroom and walked down the corridor to Dean's room; they sat next to each other on the bed.

The silence almost made Sam regret the pendulum ticking in the library.

_Another side effect_.

So was it… _normal_? Dean had already gone through this the previous year? And Sam hadn't noticed anything?

Dean was a master of deceit: it was a necessary talent in their job, but the older brother had made it into an art. It was impossible to find something that Dean wanted to keep hidden, unless the hunter was too tired or hurt to keep his mask in place; and even then, it was hard reading the real Dean.

But it was sad for Sam thinking he'd been so centered on himself, focused on his own pain and pride that he hadn't seen how sick his brother was. He felt ashamed: it the roles were reversed, Dean would've noticed.

"Dean," Sam started, unsure of what to say. He wanted to comfort his brother, but he knew words weren't enough.

"Last night, at that cabin… I didn't mean to," the older man surprisingly interrupted him. He kept his eyes on the half-closed door, determined to not meet his brother's eyes. "I tried to… hold back. I _begged _them to let me go, to not… do anything stupid. I knew I wouldn't be able to keep control if they'd provoke me. But they did. And I couldn't," he concluded in a whisper. "I'm sorry."

"It's not your fault," Sam readily said. He didn't know what bearing the Mark actually meant, he didn't know how much aware Dean was of what the demonic symbol made him do; but he knew his brother and he knew Dean would never kill – _slaughter _– other human beings, if he were aware of himself, no matter how scum they were.

"I don't know how long I'll be able to resist," Dean went on as if he hadn't heard at all. "Last time… I started being sick after you and Cas stopped me from killing Gadreel. The Mark needs to be _fed_. It craves blood." He paused. "I should've felt… _better_, not worse, after what I did. But…" He clenched his fists, closed his eyes. "The Mark wants more," he said in a low voice.

"Dean." Sam tightened his hold on his brother's shoulder, making him raising his head despite himself; his eyes, though, were still averted from his little brother's. "It's gonna be okay. We'll find a way to erase the Mark and you'll be yourself again. I promise."

"Sam…" Dean weakly protested.

"_I promise, Dean_," Sam repeated decisively, and his brother finally looked at him, saw the sincerity in his eyes.

Dean nodded.

And Sam saw that he had every right – that it was his _duty_ – to make that promise: it wasn't an empty promise, he'd save his brother. And he also knew how.

While he convinced Dean to follow him to the kitchen, where Cas was setting the table with Claire's help, his mind made a plan: he was gonna summon Crowley and, willing or not, the demon was gonna tell him how to find Cain.

Sam was ready to do anything; even threaten the king of Hell.

Even make a deal.

He was gonna save Dean.

* * *

><p><em>I know this is not the way things will go, but there are rumors about Cain coming back, and of course Crowley will cross paths with the brothers again, so this could actually be not that far from truth. In the meantime, let me dream about brotherly moments and Dean throwing up blood.<em>

_A big thank you in advance to anyone who was patient enough to read it all and an even bigger one to those who will take the time to write a line or two. I hope you enjoyed the story._

_Merry Christmas to those who celebrate, and happy holidays to everybody! :)_


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